The present invention relates to a friction vibration damper which is associated with controlling vibrations of a vibrating component and in particular, although not exclusively, a component of a gas turbine engine or a component of a machining operation.
A combustor system of a gas turbine engine comprises a combustor chamber, a transition duct and an annular distribution chamber. The transition duct transmits hot gases from the combustion chamber to the annular distribution chamber, the hot gases then proceed into a turbine stage thereby driving the turbine.
In order to meet NOx (oxides of nitrogen) and CO (carbon monoxide) emission level requirements, turbulence of a fuel and air mixture is promoted to give acceptable combustion emissions. However, increasing the turbulence during the combustion process, to reduce emission levels, causes an increase of combustor noise which leads to an increase in vibratory stresses in the combustor system components. Combustor system components are vulnerable to high cyclic fatigue failure when the natural frequency of the component coincides or is close to coinciding with the acoustic frequency of the combustion process causing resonance of the component and consequently high vibratory amplitudes and hence high stresses in the component.
During a machining operation, for instance milling a metallic component, it is common for chatter to occur if the tooling or workpiece is of insufficient rigidity. Chatter is the vibration of the milling tool relative to the workpiece which results in either a reduction in the quality of the surface finish being machined or an increase in the machining process time where a better surface finish is required. In the manufacture, for instance, of aero-engine blisks this is of particular importance as the tough nature of the material, titanium, to be machined and the flexibility and low inherent damping of the workpiece severely curtails machining rates.
European Patent Application EP00309427.3 discloses a particle vibration damper having at least one chamber filled with a high percentage volume (95%) of substantially spherical elements. Vibration energy is damped by contact friction between the elements, however, as the level of excitation increases the elements begin to move in a convection-like flow pattern. When this convection-like flow occurs the effectiveness of the damper reduces.
It is an object of the present invention to provide a friction vibration damper which reduces or substantially prevents such a convection-like flow pattern.
According to the present invention there is provided a friction vibration damper for damping the vibrations of a vibrating component comprising a body having a chamber, the chamber partially filled with a plurality of elements, the friction vibration damper, in use, disposed on or in the vibrating component wherein the friction vibration damper is configured to substantially prevent the elements operationally moving in a convection-like flow pattern.
Preferably the plurality of elements comprise substantially spherical elements. Alternatively, the plurality of elements comprises substantially spherical elements of at least two discrete sizes. Furthermore, it is preferred that the elements are substantially spherical each with a diameter in the range 0.1 to 5.0 millimeters.
Alternatively, the plurality of elements comprise elements having a high aspect ratio and comprise elongate elements.
Alternatively the plurality of elements comprise elements having a low aspect ratio and comprise disc shaped elements.
Preferably the body comprises a baffle, the baffle disposed within the chamber to substantially prevent the elements operationally moving in a convection-like flow pattern. Furthermore the baffle extends across the chamber and may comprise a mesh structure. Alternatively the baffle comprises a xe2x80x9cwire woolxe2x80x9d matrix.
Preferably the body comprises the chamber having a high aspect ratio. Alternatively the body comprises the chamber having a low aspect ratio.
Preferably the friction vibration damper is mounted on a pedestal, the pedestal attached to the vibrating component.
Alternatively the body has two or more of the chambers and furthermore each of the chambers is partially filled with a plurality of elements of substantially the same size, each plurality of elements in each chamber being of a different discrete size.
Preferably the elements are metallic, but may be ceramic.
Preferably the chamber is filled with elements to between 90 and 100 percent by volume and in particular may be filled with elements to 95 percent by volume.
Similarly each of the chambers is filled with elements to 95 percent by volume.
Alternatively each of the chambers is filled with elements to a different percentage by volume of each chamber.
Preferably the body of the friction vibration damper is substantially cylindrical. Alternatively, the body of the friction vibration damper is substantially parallelepiped.
Preferably the vibrating component is a component of a gas turbine engine. Alternatively the vibrating component is a workpiece and the workpiece is subject to a machining operation. Similarly the vibrating component may be a machine tool or may be a machine.
Alternatively the friction vibration damper is disposed to the vibrating component by temporary means.
Preferably the component vibrates in the frequency range up to 10 Hertz.
Preferably a method of damping the vibrations of a vibrating component comprising the steps of, locating the position of the greatest amplitude of vibration on an engine component and disposing a vibration damping device on the component at the position of the greatest amplitude of vibration.